The combustion chamber wall structure or nozzle wall structure is made of an outer pressure jacket and an inner wall member that in operation is in contact with the combustion hot gases. The inner wall member is conventionally provided with a multitude of cooling channels.
German Patent Publication DE 3,535,779 describes a thrust nozzle for a high performance propulsion plant, for example for carrier rockets or reusable spacecraft. The thrust nozzle has a contour of rotational symmetry providing a circular cross-section that tapers, starting from the combustion chamber, in the direction of the neck cross-section downstream of which the cross-section widens again. Such a contour of rotational symmetry is simple with regard to technical manufacturing considerations. Such contour also makes possible an effective take up of the gas forces.
Due to the high temperatures of about 3000.degree. C., however, the thrust nozzle must be effectively cooled. The known thrust nozzle comprises an inner jacket made of a copper alloy. The copper alloy inner jacket is cooled with the help of cooling channels extending either circumferentially or axially in the inner jacket or inner wall member. A cooling medium flows through these channels, for example liquid hydrogen to be used as fuel in the thrust nozzle after it has served as a coolant. The inner jacket is outwardly surrounded by a support jacket in a jointless manner. The support jacket takes up the gas pressure forces. The support jacket must have a high tension strength while its heat resistance is of lesser importance due to the inwardly arranged cooling.
Efforts have been made in the development of hypersonic aircraft equipped with such a thrust nozzle or nozzles. These thrust nozzles must generate thrust with a high efficiency, whereby several propulsion plants are to be arranged alongside one another. For achieving these requirements, it has been suggested that the cross-sectional contour of these nozzles transits from a circular cross-section in the area of the combustion chamber to a rectangular cross-section in the area of the nozzle exit or even already in the area of the nozzle neck.
Such a contour requires that the nozzle wall assumes a complicated curved configuration or shape. On the one hand the relatively soft inner jacket or inner wall member must have a precisely conforming inner contour in order to assure an optimal throughflow. On the other hand, the outer support jacket must, due to strength considerations, have such a configuration retaining stiffness that a conforming to the configuration of the inner jacket is not possible. However, the production of both jackets with such a high configuration accuracy is very expensive due to manufacturing considerations taking the complicated geometry into account.
A further disadvantage is to be seen in that after the joining of the inner and outer jacket, hollow spaces possibly remain between the jackets. In operation, these hollow spaces may lead to deformations and fractures and thus resulting in a reject.
It is known from German Patent Publication DE 4,015,204 to equip a thrust nozzle with an inner jacket made of a material having a high heat conductivity and provided with a number of cooling channels in order to avoid the above mentioned disadvantages. The inner jacket is surrounded outwardly by a rigid support jacket. An intermediate layer is cast between the inner jacket and the support jacket. The purpose of the intermediate layer is to compensate for manufacturing tolerances of the inner jacket and the support jacket so that the requirements regarding shape accuracies of both jackets can be reduced.
German Patent Publication DE 4,115,403 discloses a nozzle wall for expansion ramps and hot gas nozzles which comprise an outer support structure away from the hot gas and a multilayer inner structure provided with cooling channels spaced from one another and extending to face the hot gas. Nozzles of such a construction are suitable for achieving a high thrust and a simple switchability between the types of propulsion plants, particularly if these nozzles have a rectangular construction. However, nozzle walls of such thrust nozzles are exposed to high pressure forces and temperatures. Contrary to walls of nozzles with circular cross-section, the pressure forces effective on plane nozzle walls of rectangular nozzles or combustion chambers cause high bending moments. Thus, warping or undesirable stress distributions may occur in the rectangular thrust nozzle, whereby the intended function of the thrust nozzle is jeopardized. Additionally, the so-called bi-metal effect has an aggravating influence due to the temperature differences within the multilayered wall. Thus, dimensionally stable cooled walls are required in order to avoid thrust losses and leakage currents.
In view of the above the known nozzle wall comprises an internal structure including a heat conducting layer in contact with the hot gas and a heat resistant sliding layer, whereby the cooling channels are embedded in the heat conducting layer. The heat conducting layer is elastically connected with the support structure by a plurality of holding elements penetrating the sliding layer. As a result, the sliding layer can be made of granular ceramic material while the heat conducting layer is made of copper.
The holding elements may be constructed in the shape of small tubes, whereby however, the available expansion length is insufficient, due to the required minimal stiffness of these small tubes, when the thrust nozzle is exposed to the extreme thermal loads that are usual in high performance propulsion plants, due to the high induced thermal stresses accompanied by substantial plastic strains whereby the useful life is substantially reduced.
The above useful life limitation is due to a failure, such as a fracture, in the combustion chamber wall after a limited number of load cycles causing a respective plastic deformation and creep due to the restrained thermal strains or expansions that are caused by secondary stresses resulting from the high thermally induced stresses amounting to about 80% of the entire load.
The foregoing drawbacks not only limit the reusability, but also increase the total costs of the conventional carrier system. Fracture formations cause impulse losses and excessive loads on the propulsion plant components including known turbo pumps during the operation of the propulsion plant.
Even if other materials for the intermediate layer between the hot gas exposed wall and the outer structure are used, such as sintered aluminum or foamed aluminum materials which can take up high deformations, irreversible deformations in the plastic range occur so that these characteristics lead to the single use concept.
Known materials for use in the support elements between the hot gas exposed wall and the outer support structure surrounding the gas exposed wall are supposed to provide a defined yielding by cross-expansion during operation of the high performance propulsion plant. However, these support elements do not have a sufficiently elastic expansion or strain characteristic.